The present invention relates to robot arm drive systems, particularly systems for handling wafers in the semiconductor manufacturing industry.
Current robot arm systems include drive systems for independently controlling the extension of the arm, rotation of the arm, rotation of the grasping tool on the end of the arm and other movements in various different angular directions as are necessary to provide the necessary flexibility to perform numerous different maneuvers on, and manipulations of, items held by the robot hand. Certain robot systems also include telescoping mechanisms to extend the arm or to elevate the arm and related assemblies. Typically the operative end of the arm is equipped with an end effector or mechanical hand for holding or grasping an item such as a silicon wafer, computer hard disc, compact disk or other flat, touch sensitive product. The most common end effector uses one or more vacuum outlets which contact the surface of the wafer. However, more recently edge gripping systems are coming into use.
U.S. Pat. No. 4,897,015 to Abbe et al. describes a rotary-to-linear motion robot arm that uses a first motor to control a multi-linkage robot arm to produce straight line radial motion from motor-driven rotary motion. An additional motor may be coupled to the robot arm for operation independent of that of the first motor to angularly move the multi-linkage robot arm without radial motion. Because they independently produce radial motion and angular motion, the first and second motors produce useful robot arm movement when either one of them is operating. The robot arm of the Abbe et al. patent extends and retracts an end effector (or a hand) along a straight line path by means of a mechanism that pivotally couples in a fixed relationship a first arm portion (or aft arm) and a second arm portion (or forearm) so that they move in predetermined directions in response to rotation of the aft arm. To achieve angular displacement of the hand, a theta. drive motor rotates the entire robot arm structure.
U.S. Pat. No. 5,007,784 to Genov et al. describes a robot arm with an end effector structure that has two oppositely extending hands, each of which is capable of picking up and transporting a specimen. The end effector structure has a central portion that is centrally pivotally mounted about the distal end of a second link or forearm.
The robot arm structures of the Abbe et al. and Genov et al. patents operate similarly, in that each of the end effector structures picks up and transports specimens by using one motor to extend and retract a hand and another, different motor, to rotate the entire robot arm structure, to allow the hand to extend and retract at different ones of a restricted number of angular positions.
U.S. Pat. No. 5,741,113 to Bacchi et al is directed to a multiple link robot arm mechanism that uses two motors capable of synchronized operation to permit movement of the robot arm hand along a curvilinear path as the extension of the hand changes. A first motor rotates a forearm about an elbow axis that extends through distal and proximal ends of the aftarm and forearm arm respectively, and a second motor rotates the aftarm about a shoulder axis that extends through a proximal end of the aftarm. A mechanical linkage couples the aftarm and the forearm. The mechanical linkage forms an active drive link and a passive drive link. The active drive link operatively connects the first motor and the forearm to cause the forearm to rotate about the elbow axis in response to the first motor. The passive drive link operatively connects the forearm and the hand to cause the hand to rotate about a wrist axis in response to rotation of the forearm about the elbow axis. The wrist axis extends through distal and proximal ends of the forearm and hand, respectively.
Two major problems exist with currently available robots. First, robots with motors below the base plate perform only highly restricted radial, angular moves. Secondly, robots capable of X, Y, Z and Theta movement carry the drive motors above the base mounting flange and at the arm joints, resulting in a unit with a high inertia and sluggish response as well as a tendency to wear and, as a result, generate particles in the vicinity of the arm.
The current invention provides an arrangement, which allows completely independent movement of each arm element and also keeps all of the drive motors below the base plate of the system. This provides a much cleaner, streamlined arrangement, which is better balanced, and provides for a much more structurally rigid assembly. The new motor mounting arrangement allows for easy tensioning of drive belts as well as easy and rapid replacement of drive motors or belts if they should happen to malfunction.
The design incorporates multiple concentric spindles with a common central axis, all of the spindles being mounted on a single frame. Each spindle is separately driven and each controls a different linkage or arm portion. Because of this concentric assembly the drive assembly is easier to assemble, requires fewer parts and costs less to build, has a lower inertia, wear is reduced, the operation of the robot is quieter and it responds more quickly to signals from the electronic control unit.
Another unique aspect of the invention is the mechanical arrangement, which provides a multi-turn rotational hard stop for each of the nested spindles.
A still further aspect of the invention is a belt tensioning mechanism in the arm which delivers symmetrical outward forces on the belts eliminating creep of drive belts seen in prior art systems.